This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. A computational study is proposed to determine the mechanism of intracellular sterol transport via a protein-assisted nonvesicular pathway. Although much research has focused on extracellular transport of sterols, such as cholesterol in lipoproteins, it is our aim to describe the mechanism of transport from where sterols are made in the cell (endoplasmic reticulum, ER) to the plasma membrane (PM). Our microsecond simulations will be on a yeast oxysterol binding protein (Osh4) and its interactions with the ER and PM. It is our aim to describe protein attachment to these membranes that contain important signaling lipids, known as phosphoinositides. Our previous studies on sterol binding and lipid docking demonstrate that we are at the stage to begin these computationally extensive molecular dynamics simulations. It is our plan to initially investigate single membrane interaction with Osh4, but our ultimate objective is to use a dual membrane model to simulate the experimentally suggested lipid tethering mechanism used by Osh4 to transport sterols. We will also test the experimental hypothesis that this protein can pivot between the ER and PM to transport sterols. Ultimately, these simulations will not only clarify what is seen experimentally for yeast, but also suggest mechanisms for sterol transport in humans with the homologous ORP proteins.